Ion implantation is a standard technique for introducing conductivity-altering impurities into substrates. A desired impurity material is ionized in an ion source, the ions are accelerated to form an ion beam of prescribed energy, and the ion beam is directed at the surface of the substrate. The energetic ions in the beam penetrate into the bulk of the substrate material and are embedded into the crystalline lattice of the substrate material to form a region of desired conductivity.
Solar cells provide pollution-free, equal-access energy using a free natural resource. Due to environmental concerns and rising energy costs, solar cells, which may be composed of silicon substrates, are becoming more globally important. Any reduced cost to the manufacture or production of high-performance solar cells or any efficiency improvement to high-performance solar cells would have a positive impact on the implementation of solar cells worldwide. This will enable the wider availability of this clean energy technology.
Solar cells typically consist of a p-n semiconducting junction. FIG. 1 is a cross-sectional view of a selective emitter solar cell. It may increase efficiency (e.g. percentage of power converted and collected when a solar cell is connected to an electrical circuit) of a solar cell 210 to dope the emitter 200 and provide additional dopant to the regions 201 under the contacts 202. More heavily doping the regions 201 improves conductivity and having less doping between the contacts 202 improves charge collection. The contacts 202 may be spaced approximately 2-3 mm apart. The regions 201 may only be approximately 100-300 μm across. FIG. 2 is a cross-sectional view of an interdigitated back contact (IBC) solar cell 220. In the IBC solar cell, the junction is on the back of the solar cell 220. The doping pattern is alternating p-type and n-type dopant regions in this particular embodiment. The p+ emitter 203 and the n+ back surface field 204 may be doped. This doping may enable the junction in the IBC solar cell to function or have increased efficiency.
Both the selective emitter solar cell of FIG. 1 and the IBC solar cell of FIG. 2 have an anti-reflective coating (ARC) 205. This ARC 205 may be, for example, SixNy. To improve the light capture of the ARC layer 205, the SixNy layer may have an oxide film 206 underneath. The oxide film 206 may have a higher refractive index than silicon. The SixNy ARC 205 may have a higher refractive index than the oxide 206 and further refracts light back into the silicon of the solar cell. This type of refraction reduces the amount of reflected light and increases cell efficiency.
Use of an oxide layer 206 with an ARC 205 has drawbacks. Carrier recombination occurs at the surface interfaces, such as at the dangling bonds between the silicon and the dielectric layers (i.e. the ARC 205 and oxide layers 206). Furthermore, the light trapping is not optimal and the dielectric layers, such as the nitride or oxide layer, absorb UV light. This reduces UV collection efficiency of the solar cell. Accordingly, there is a need in the art for improved methods that enhance optical properties of a dielectric layer of a solar cell.